It is often desirable to index documents so that parts can be found quickly or easily. Examples include dictionaries or directories where one wishes to find a particular letter, Bibles where it is desirable to easily find various books, cook books, account books, photo albums, travel guides and the like.
For many years it has been common to provide such books with tapering notches on the edges of the pages to expose letters, names of the books of the Bible or other indicia. Such notches are costly to make and are infeasible to add to books a person already has. Such notches are also unidirectional. The indicia in the notches may be seen from only the front of the book, for example, and cannot be seen from the back. Some particularly thick books such as unabridged dictionaries may have some of the notches facing the front and some facing the back so that when the book is open in the middle, the letters in the notches are all visible. This means, of course, that when the book is open any place but the middle, at least some of the indicia in the notches are hidden.
It can therefore be desirable to provide adhesive tabs that can be applied to books extending beyond the edges of the pages so that indicia can be seen from both sides.
A variety of tabs have been proposed. Some are in the form of Y-shaped strips where the two arms of the Y can be glued to opposite faces of a book page with the leg of the Y extending beyond the edge. These tend to be somewhat costly and are often thick so that they add substantial bulk along the edge of the book. It is also difficult to make these with pressure sensitive adhesive since the parts may inadvertently stick to each other. The usual tabs of this type have water activiated glues.
Another type of tab has a pressure sensitive adhesive along part of one face to adhere to a page with an unglued edge of the tab extending beyond the edge of the page. The front face of such a tab can be preprinted but the back adjacent the backing sheet cannot be readily printed. Thus, the tab has one of the shortcomings of the index notches. A significant disadvantage of this type of index tab is the difficulty in aligning the edge of the adhesive with the edge of the page. If the adhesive does not come to the edge of the page, a bothersome gap is left. Worse, if the adhesive extends beyond the edge of the page, it collects dirt and lint, and rapidly becomes quite unsightly.
Still another type of book index tab comprises a transparent film with pressure sensitive adhesive on its lower face. A pair of strips of paper bearing indicia such as books of the Bible are adhered to the adhesive so that the indicia can be seen through the transparent film. The two strips of paper are parallel and centered on the index tab with a gap between the two strips. This assembly is mounted on a backing sheet with a release coating. When the tab is used, it is peeled from the backing and the edge of one of the pieces of paper is abutted against the edge of the page to which the tab is secured. The tab is then folded along the gap between the two strips of paper and the other half of the tab adhered to the opposite face of the page. Such tabs are costly to make because of the extra strips of paper between the label stock and the backing.
Some of these types of tabs generally suitable for the purpose are undesirable since they are unattractive or opaque so as to obscure text when the page of the book has a narrow margin.
Index tabs as provided in practice of this invention are made from stock of the sort used for pressure sensitive labels and the like. Such stock is readily commercially available in a broad variety of forms from a number of vendors. One difficulty with pressure sensitive labels is that it is sometimes hard to peel the self-adhesive label from the backing sheet. It can sometimes be frustrating to start the peeling since the label and backing are virtually uniformly flexible and it is difficult to get a fingernail or the like in the narrow interface between the label and the backing. Starting peeling is particularly difficult when the edges of labels abut each other with only a die-cut line with essentially no space between adjacent labels.
A variety of techniques have been used to alleviate this problem. For example, matrix cut labels are sometimes used where the matrix surrounding individual labels is removed to leave labels as isolated islands on the backing. When such labels are slightly stiffer than the backing, peeling can be initiated by bending. This is not easily accomplished when the label is itself quite thin and flexible.
In some cases the backing sheet has been weakened along diagonally extending lines by deeply scoring the backing sheet or chemically attacking the backing sheet, so that upon bending, the backing sheet breaks to permit easy peeling from the overlying label. Such score lines intentionally damage the backing to a degree that causes it to break upon bending or creasing. Such breakage lines bear no relation to the indicia printed on the label.
Thus, it is desirable to provide index tabs for books or other documents which are quite thin to avoid adding excess bulk to the edges of book pages, can be read from both faces, do not obscure text of the book, can be easily aligned with the edges of the pages to give a neat appearance, can be readily removed from the backing sheets on which the tabs are supplied, can be easily applied to books one already possesses, and are economical to make and sell.